[Ocfs2-devel] [PATCH v2] ocfs2: try a blocking lock before return AOP_TRUNCATED_PAGE

[alex chen <alex.chen@huawei.com>]

Hi Gang,

It looks good to me.

Thanks,
Alex


On 2017/12/28 15:48, Gang He wrote:
> If we can't get inode lock immediately in the function
> ocfs2_inode_lock_with_page() when reading a page, we should not
> return directly here, since this will lead to a softlockup problem
> when the kernel is configured with CONFIG_PREEMPT is not set.
> The method is to get a blocking lock and immediately unlock before
> returning, this can avoid CPU resource waste due to lots of retries,
> and benefits fairness in getting lock among multiple nodes, increase
> efficiency in case modifying the same file frequently from multiple
> nodes.
> The softlockup crash (when set /proc/sys/kernel/softlockup_panic to 1)
> looks like,
> Kernel panic - not syncing: softlockup: hung tasks
> CPU: 0 PID: 885 Comm: multi_mmap Tainted: G L 4.12.14-6.1-default #1
> Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> Call Trace:
>   <IRQ>
>   dump_stack+0x5c/0x82
>   panic+0xd5/0x21e
>   watchdog_timer_fn+0x208/0x210
>   ? watchdog_park_threads+0x70/0x70
>   __hrtimer_run_queues+0xcc/0x200
>   hrtimer_interrupt+0xa6/0x1f0
>   smp_apic_timer_interrupt+0x34/0x50
>   apic_timer_interrupt+0x96/0xa0
>   </IRQ>
>  RIP: 0010:unlock_page+0x17/0x30
>  RSP: 0000:ffffaf154080bc88 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff10
>  RAX: dead000000000100 RBX: fffff21e009f5300 RCX: 0000000000000004
>  RDX: dead0000000000ff RSI: 0000000000000202 RDI: fffff21e009f5300
>  RBP: 0000000000000000 R08: 0000000000000000 R09: ffffaf154080bb00
>  R10: ffffaf154080bc30 R11: 0000000000000040 R12: ffff993749a39518
>  R13: 0000000000000000 R14: fffff21e009f5300 R15: fffff21e009f5300
>   ocfs2_inode_lock_with_page+0x25/0x30 [ocfs2]
>   ocfs2_readpage+0x41/0x2d0 [ocfs2]
>   ? pagecache_get_page+0x30/0x200
>   filemap_fault+0x12b/0x5c0
>   ? recalc_sigpending+0x17/0x50
>   ? __set_task_blocked+0x28/0x70
>   ? __set_current_blocked+0x3d/0x60
>   ocfs2_fault+0x29/0xb0 [ocfs2]
>   __do_fault+0x1a/0xa0
>   __handle_mm_fault+0xbe8/0x1090
>   handle_mm_fault+0xaa/0x1f0
>   __do_page_fault+0x235/0x4b0
>   trace_do_page_fault+0x3c/0x110
>   async_page_fault+0x28/0x30
>  RIP: 0033:0x7fa75ded638e
>  RSP: 002b:00007ffd6657db18 EFLAGS: 00010287
>  RAX: 000055c7662fb700 RBX: 0000000000000001 RCX: 000055c7662fb700
>  RDX: 0000000000001770 RSI: 00007fa75e909000 RDI: 000055c7662fb700
>  RBP: 0000000000000003 R08: 000000000000000e R09: 0000000000000000
>  R10: 0000000000000483 R11: 00007fa75ded61b0 R12: 00007fa75e90a770
>  R13: 000000000000000e R14: 0000000000001770 R15: 0000000000000000
> 
> About performance improvement, we can see the testing time is reduced,
> and CPU utilization decreases, the detailed data is as follows.
> I ran multi_mmap test case in ocfs2-test package in a three nodes cluster.
> Before apply this patch,
>   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
>  2754 ocfs2te+  20   0  170248   6980   4856 D 80.73 0.341   0:18.71 multi_mmap
>  1505 root      rt   0  222236 123060  97224 S 2.658 6.015   0:01.44 corosync
>     5 root      20   0       0      0      0 S 1.329 0.000   0:00.19 kworker/u8:0
>    95 root      20   0       0      0      0 S 1.329 0.000   0:00.25 kworker/u8:1
>  2728 root      20   0       0      0      0 S 0.997 0.000   0:00.24 jbd2/sda1-33
>  2721 root      20   0       0      0      0 S 0.664 0.000   0:00.07 ocfs2dc-3C8CFD4
>  2750 ocfs2te+  20   0  142976   4652   3532 S 0.664 0.227   0:00.28 mpirun
> 
> ocfs2test at tb-node2:~>multiple_run.sh -i ens3 -k ~/linux-4.4.21-69.tar.gz -o 
> ~/ocfs2mullog -C hacluster -s pcmk -n tb-node2,tb-node1,tb-node3 -d 
> /dev/sda1 -b 4096 -c 32768 -t multi_mmap /mnt/shared
> Tests with "-b 4096 -C 32768"
> Thu Dec 28 14:44:52 CST 2017
> multi_mmap..................................................Passed.
> Runtime 783 seconds.
> 
> After apply this patch,
>   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
>  2508 ocfs2te+  20   0  170248   6804   4680 R 54.00 0.333   0:55.37 multi_mmap
>   155 root      20   0       0      0      0 S 2.667 0.000   0:01.20 kworker/u8:3
>    95 root      20   0       0      0      0 S 2.000 0.000   0:01.58 kworker/u8:1
>  2504 ocfs2te+  20   0  142976   4604   3480 R 1.667 0.225   0:01.65 mpirun
>     5 root      20   0       0      0      0 S 1.000 0.000   0:01.36 kworker/u8:0
>  2482 root      20   0       0      0      0 S 1.000 0.000   0:00.86 jbd2/sda1-33
>   299 root       0 -20       0      0      0 S 0.333 0.000   0:00.13 kworker/2:1H
>   335 root       0 -20       0      0      0 S 0.333 0.000   0:00.17 kworker/1:1H
>   535 root      20   0   12140   7268   1456 S 0.333 0.355   0:00.34 haveged
>  1282 root      rt   0  222284 123108  97224 S 0.333 6.017   0:01.33 corosync
> 
> ocfs2test at tb-node2:~>multiple_run.sh -i ens3 -k ~/linux-4.4.21-69.tar.gz -o 
> ~/ocfs2mullog -C hacluster -s pcmk -n tb-node2,tb-node1,tb-node3 -d 
> /dev/sda1 -b 4096 -c 32768 -t multi_mmap /mnt/shared
> Tests with "-b 4096 -C 32768"
> Thu Dec 28 15:04:12 CST 2017
> multi_mmap..................................................Passed.
> Runtime 487 seconds.
> 
> Fixes: 1cce4df04f37 ("ocfs2: do not lock/unlock() inode DLM lock")
> Signed-off-by: Gang He <ghe@suse.com>

Reviewed-by: Alex Chen <alex.chen@huawei.com>

> ---
>  fs/ocfs2/dlmglue.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 4689940..5193218 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -2486,6 +2486,15 @@ int ocfs2_inode_lock_with_page(struct inode *inode,
>  	ret = ocfs2_inode_lock_full(inode, ret_bh, ex, OCFS2_LOCK_NONBLOCK);
>  	if (ret == -EAGAIN) {
>  		unlock_page(page);
> +		/*
> +		 * If we can't get inode lock immediately, we should not return
> +		 * directly here, since this will lead to a softlockup problem.
> +		 * The method is to get a blocking lock and immediately unlock
> +		 * before returning, this can avoid CPU resource waste due to
> +		 * lots of retries, and benefits fairness in getting lock.
> +		 */
> +		if (ocfs2_inode_lock(inode, ret_bh, ex) == 0)
> +			ocfs2_inode_unlock(inode, ex);
>  		ret = AOP_TRUNCATED_PAGE;
>  	}
>  
>